"[Dunbar] found that the same human brain can only maintain relationships of increasing closeness in inverse proportion." #readingToday

The number 150 became known as the Dunbar number but, in fact, Dunbar's work continued and he revealed a hierarchy of numbers associated with a human brain size, that is very interesting. By studying different kinds of human groups, he found that the same human brain can only maintain relationships of increasing closeness in inverse proportion. The more intimate the relationship, the more work it costs us, and the fewer we can manage. He found that we manage around 5 intimate relationships, around 15 in a family-like group, about 30-40 in a tribal or departmental working relationship, and 100-150 general acquaintances. Whatever semantics we associate with a group, i.e. whether we consider someone close a lover or a bitter enemy , family or team , it is the level of cognitive processing, or intimacy, that limits the number we can cope with. Once again, dynamics trump semantics: the brain seems to have a scale which has a limiting processing threshold._

In Search of Certainty, Mark Burgess, 2013